Emissivity is the ratio of the radiation emitted by the model’s surface to the radiation emitted by a blackbody at the same temperature. It is the relative ability of a model’s surface to emit energy through radiation. Emissivity is independent of the wavelength of the radiation and the direction. Type a value between 0 and 1 to define the emissivity of the radiation condition. The default value for emissivity is 1 without any units. You can define emissivity as varying spatially or as a function of temperature.